The present invention relates to a method and to a device for automatically monitoring a flight path of an aircraft during a required navigation performance operation of an aircraft, in particular a transport airplane.
Although not exclusively, the present invention applies more particularly to required navigation performance with authorization required (RNP AR) operations. These RNP AR operations are based on area navigation (RNAV) and on required navigation performance (RNP) operations. They have the distinctive feature of requiring special authorization in order to be implemented on an aircraft.
It is known that the aircraft is provided with monitoring and alert means allowing it to be ensured that said aircraft remains in a corridor, referred to as RNP, around a prescribed path. Outside of this corridor, there are potentially hilly or mountainous areas or other aircraft. The required performance for an RNP-type operation is defined by an RNP value which represents the half-width (in nautical miles (NM)) of the corridor around the reference path in which the aircraft must remain for 95% of the time during operation. A second corridor (around the reference path) of a half-width of twice the RNP value is also defined. The probability that the aircraft will leave this second corridor has to be less than 10-7 per flight hour. The concept behind RNP AR operations is yet more restrictive. The RNP AR procedures are in fact characterized in particular by RNP values which are less than or equal to 0.3 NM on approach, and which may drop as far as 0.1 NM.
Demonstrating that avionics systems allow RNP-type operations to be carried out with sufficient availability and precision is based on a statistical analysis of the different sources of error which may lead to a discrepancy between the position of the aircraft and the procedure as published on the approach charts.
Three separate sources are considered to characterize the aggregate error: an error in defining (or in calculating) the path, an error in navigation (position calculation) and an error in guidance.
During a required navigation performance operation, the position of the aircraft is monitored in real-time, and an alarm is sounded to the crew when the aircraft departs beyond an acceptable limit from the path extracted from an on-board navigation database.
In order to guard against possible coding errors in the navigation database (NDB), airlines whose aircraft implement such operations are required to validate the database each time the data is updated, currently every twenty-eight days (AIRAC cycle). In practice, this validation may be carried out on simulators of the airline by flying each RNP approach in the database that the airline wishes to operate and by ensuring that, in each case, the path flown on the simulator conforms to the published procedure.
However, this verification, which is carried out on the ground, only allows coding errors in the database to be remedied, and not extraction or corruption errors when loading the data onto the flight management system of the aircraft that is intended to calculate the flight path. In addition, guidance on the corresponding flight path and monitoring in real-time carried out at the current position of the aircraft are only relevant if the procedure loaded onto aircraft systems and then the calculation of the path are consistent. If the procedure is corrupted during or after loading or if the flight management system calculates an incorrect path, the problem is thus identified owing to the expertise of the crew (comparison with the approach charts or experience of the procedure), which allows the problem to be identified.
The problem addressed by the present invention is that of improving the integrity of the guidance based on published procedure during required navigation performance operations, in particular RNP AR operations having low values (less than 0.3, for example).